Abstract:The changes of soil physical and chemical properties at different developmental stages (6, 15, 23, and 35 years old) of larch (Larix kaempferi Carr.) plantations were investigated and analyzed with chronosequence method in the forest area of Xiaolongshan in Gansu Province. By the method of principal component analysis, the integrated fertility indexes for larch plantations were calculated taking the contribution rate of each principal component character as weight. The results showed that the soil physical and chemical properties were deteriorated in the pre-mature stands with the growth of larch plantations. For example, the soil bulk density increased to 1.62 g·cm-3, the capillary porosity and maximum moisture capacity decreased to 29.69% and 24.45%, while the amounts of soil organic matter, nitrogen, phosphorus, potassium, magnesium and calcium decreased. The soil properties from pre-mature to mature forest stage showed the value of soil physical and chemical properties recovered, such as the soil bulk density decreased to 1.21 g·cm-3, the capillary porosity and maximum moisture capacity increased to 45.56% and 42.65%, and the amounts of soil nutrient returned to high level, even much higher than the level of the middle age forest. The integrated fertility indexes (IFI) of the soil were -0.329, 0.188, -0.565 and 0.739 in the young, middle, pre-mature, and mature plantations respectively, so the soil properties of pre-mature forest displayed the worst values, while those of the mature was the best.